Control device



Hug-Jr- 4 Feb. 6, 1962 WITNESSES%QL V. L. CARISSIMI CONTROL DEVICE FiledDec. 14, 1956 INVENTOR Vincent L. Corissimi.

ATTORNFY United States Patent 3,020,381 CONTROL DEVICE Vincent L.Carissimi, Fairfield, Conn, assignor to Westinghouse ElectricCorporation, East Pittsburgh, Pin, a corporation of Pennsylvania FiledDec. 14, 1956, Ser. No. s2s,422

I 16 Claims. (Cl. 219-20) My invention relates to a device forcontrolling an electrical circuit and more particularly to a deviceforcontrolling the electrical energization of an electrical heating unitin an electric range.

In. the art of cooking, the particular temperature at which a food ormixture should be cooked varies due to the variations of the matter ofthe various foods and nrixlures. For a particular food or mixture,however, there is a particular optimum temperature range at which thecooking process should be performed. Obviously, therefore, the heatoutput of a heatingunit, such as an electrical heating unit, must bevariable in order to obtain the various particularly desiredtemperatures. In addition, it is desirable that the desired temperaturesbe achieved as rapidly as possible, and thereafter only sutlicient heatbe supplied to maintain the food or mixture at the desired temperaturewithout the necessity of manual adjustment of the heat output of theheating unit.

Heretofore, various controls for such purposes have been developed whichhave not been entirely satisfactory due to their expensive componentsand the requisite calibration for proper operation. Other prior devicesof simplified construction have not been satisfactory as they theheating element 2 is merely representative of the various types ofstandard heating elements commercially available, and that my inventionmay be utilized with any of such heating elements at any desiredoperating voltage. A three-line supply system is commonly em ployed,accordingly, the conductors L and L are shown with a third groundedneutral conductor N as an electrical supply.

As also shown, the heating element 2 is adapted to support a cookingvessel 8 on its upper surface and is pro vided with a central opening inwhich a control unit core structed in accordance with the principles ofmy invention is located. Although not shown, the heating element 2 isstationarily supported by suitable means, such as the frame of anelectric range, in a Well-known manner. Further, it is who realized thatwater is a common cooking fluid employed and that at standardatmospheric conditions the boiling temperature of water is 212 F. Theboiling point of Water varies with variations in atmospheric conditionsso that it is necessary for a range manufacturer to supply a controlunit which will function under all normally encountered atmosphericconditions As shown, the control device comprises an inverted cup-shapedsensor plate 12, the upper surface of which is have not given consistentoperation due to various reasons such as contact wear, high currentrequirement or ambient temperature effects.

Accordingly, one object of my invention is to provide a new, improvedand simplified control device for accurately varying the heat output ofa heating element.

A more particular object of my invention is to provide a new andimproved control device comprising a pair of tandem mounted bimetalswhich are connected to each other by means of an insulator.

Still another object of my invention is to provide a new and improvedcontrol device comprising a pair of tandem mounted bimetals which areconnected to each other by means of an insulator with one end of onebimetal being rigidly secured to a heat source and the other bimetabeing movable to make and break an electrical circuit.

A further object of my invention is to provide a new and improvedcontrol device comprising a pair of tandem mounted bimetals which areconnected to each other by means or" an insulator and which bimetalsmove in opposite directions due to changes in their temperature.

These and other objects of my invention will become more apparent uponthe consideration of the following detailed description of a preferredembodiment thereof, when taken in conjunction with the attached drawing,in which a cross-sectional view of a heating element is shown having acontrol. device constructed in accordance with the principles of myinvention located therein, and the electrical control circuit thereof.

The use of electrical resistance heating elements, and particularlythose for electrical ranges for which my control is ideally suited, areWell known in the art, and accordingly, their construction and operationneed not be described in detail. In the drawing, an electrical heatingelement 2 is shown, which has as its opposite ends electricallyconnected by means of suitable electrical conductors 4 and 6 to suitableelectrical supply conductors L and L respectively. As is customary,suitable terminals T and T are provided for securing conductors 4 and 6to the conductors L and L and the heating element 2, respectively. It isto be realized that the particular showing of biased into engagementwith the bottom of the vessel 8 as hereinafter described. The sensorplate 12 is preferably formed from a hi h heat conductivity and highcreep strength material, such as stainless steel, which is resistant tothe corrosive efiiects of food spillage which may occur during thecooking process. A generally L-shape d sensorbimetal 14 is locatedcentrally of the underside of the sensor plate 12 with one of its legsbeing secured to the undersurt'ace thereof in any suitable manner suchas by being resistance welded or brazed thereto. An elongated controlbimetal 16 is located so as to be in alignment with the free leg of thesensor bimetal 14 and is supported from the free leg of the sensorbimetal 14 bya suitable support 18 so as to be both thermally andelectricallyinsulated. from the sensor bimetal 14. The particularsupport 18 for thermally and electrically insulating the bimetals l4 and16 does not constitute a part of this invention; however, one desirablemethod of accomplishing this purpose is to'secure transverselyextendingrods to the adjacent ends of the bimetals 14 and 16, in anysuitable manner such as by brazing or welding thereto, and thereaftersecuring the free ends of each of the rods together by means of a glassseal. Such rods may be made from any well-knownmaterial such as alloysidentified by thetrademark Kovar of the Westing house ElectricCorporation which has substantially the same coefficient of expansion asthe sealing glass, whereby the seal between the rods and the glass Willnot be ad-' versely affected by the thermal stresses induced therein dueto the operation of the control device 10 at elevated temperatures. Fora more particular description and showing of such a support reference ismade herein to the copending application of George W. Nagel entitledControl Device, filed May 22, 1957, Serial No. 666,869, and which hasbeen assigned to the same assignee as this invention. p I

The bimetals 14 and 16 may be made from any suitable pair of dissimilarmaterials having difierent cocfiicients is secured to the binietal 16 inany suitable manner such as by being welded, brazed or riveted thereto.The contact 2-9 is cooperable with a contact 22 of a material similar tothat of contact 29 and which is adjustably secured to a generallyL-shaped electrical conducting support 24 formed from a suitableelectrical conducting material, such as an alloy of copper. it will benoted that the contact 22 is provided with an outwardly extendingthreaded shank 26 which threadedly engages an opening, not shown, in oneleg of the support 24. The free end of shank 26 is provided withsuitable engaging means such as a diametrically extending slot 27,whereby the position of the contact 22 with respect to the one leg ofthe support 24, and consequently the other contact 20, may be varied insmall amounts. Accordingly the bimetal 16 which supports the contact 20is formed from a resilient bimetallic material as is well known.Although this particular simplified adjustable contact 22 has beendescribed, it is to be realized that other suitable adjustable means maybe utilized between the support 24 and the contact 22. As will be morefully described hereinafter contact 2 is initially located to engage thecontact 26 so that a pressure exists therebetween.

The other leg of the support 24 is rigidly secured in any suitablemanner, such as by riveting, to a support 23 located below the free endof the control biinetal 16* and which is preferably formed of a hightemperature insulating material. The support 28, in turn, is rigidlysecured to the underside of the sensor plate 12 in any suitable manner,and, as shown, a plurality of upwardly extending tie rods 29 are securedto both the support 28 and the underside of the sensor plate 12 adjacentthe fixed leg of the sensor bimetal 14. The particular manner ofsecuring the ends of the tie rods 29 to the underside of the sensorplate 12 may be accomplished in various wellknown manners such asbending the ends of the tie rods 29 transversely and soldering, brazingor welding said transversely extending parts to the underside of thesensor plate 12. p

In order to obtain proper contact of the sensor plate 1.2 with theunderside of the vessel 8 and to prevent the aforedescribed assemblyfrom being fouled due to spillage, a cylindrical shield 34) is providedwhich is rigidly secured to the aforementioned frame, not shown, towhich the heating element 2 is secured, and is also supported thereby.The shield 39 is formed preferably from a suitable corrosionesistantmaterial such as stainless steel or aluminum, and is located so as toextend around the bimetals 14 and i6 and the support 24 with its upperedge being located closely adjacent the underside of the sensor plate12, and with its lower edge being spaced below the support 24. Theshield 30 is provided with inwardly extending supporting lugs 32 spacedaround its periphery for receiving the bottom coil of a biasing spring34 on their upper edge. Spring 34 is formed of any suitable springmaterial which does not lose its resiliency at elevated temperatures,such as stainless steel, so that it is capable of withstanding theinduced thermal stresses produced by its alternate heating and coolingand is also resistant to corrosion. The upper coil of spring 34 engagesthe undersurface of the sensor plate 12 and extends around the tie rods2? so as to bias the upper surface of the sensor plate 12, upwardly intoengagement with the lower surface of the vessel 8. As can beappreciated, such positive engagement between the vessel 8 and the uppersurface of the sensor plate 12 is desirable to insure good thermaltransfer from the vessel to the sensor plate. In view of the fact thatthe bimetals 14 and 16, and supports 24 and 28 are rigidly secured tothe sensor plate 12, it is obvious that they will be moved in the samemanner by spring 34- 'as the sensor plate 12.

in order to obtain selective control of the operation of the controlbimetal 16, a heater coil 36, of any suitable electrical resistancewire, is wound about the bhnetal 16 in the well-known manner andinsulated therefrom. The heater coil 36 has one of its ends electricallyconnected by means of a suitable conductor 38 to another suitableelectrical conductor 4% having one of its ends connected to theconductor 6. The other end of the heater coil 36 is electricallyconnected by a suitable electrical conductor 41 to the supply conductorN. Again a suitable terminal T may be employed for such purpose. Asshown, the electrical conductor .1 is also electrically connected to thebimetal 16.

It will be noted that the heater coil 36 is connected between the supplyconductors L and N so as to be operative regardless of energization ofthe heater coil 2. In order to vary the electrical input to the heatercoil 36, a resistor 46 is connected to the conductor 6 and an adjustabletap 48 is electrically connected to the conductor 41 by means of asuitable electrical conductor 51. The tap 43 adjustably engages theresistor 46 so as to provide, in conjunction with the resistor 46, avariableresister in parallel with the heater coil. 36. It is alsodesirable that the conductor 6 be provided with an on-off switch so thatthe one side of the heater coil 2 may be disconnected from the line LAccordingly, a switch S having spaced contacts in the conductor 6 isprovided which is located between the resistor 46 and the line L. SwitchS may be of any conventional type; however, in order to eliminateduplication of switches, switch S is prefer-ably provided both with anon-off position and can be moved further to obtain adjustment of the tap4% across the resistor 46. With such a construction, and by placing asuitably marked identification plate in juxtaposition with handle 43 ofthe switch S, the handle 43 may be moved to a given position so as toboth electrically connect the heater 36 across the lines L and N and toalso move the adjustable tap 48 to the desired operating position withrespect to the resistor d6.

As also shown, conductor 4 is provided with a pair of normally openspaced contacts 50, similar to contacts 20 and 22, which are adapted tobe electrically bridged by teams of a movable contact 52. The operationof the movable contact 52 is obtained by means of a bimetal 54 which issimilar in construction to the bimetals 1e and 16 previously described,and around which a heater coil 56 is disposed, similar to the heatercoil 56 and in the same manner. One end of the bimet-al 54 is secured byany suitable means to the aforementioned supporting frame, and its otherend is movable into engagement with the movable contact 52 to cause themovable contact 52 to bridge the contacts 50 when the bimetal S4 isheated. Accordingly, the low expansion side of bimetal 54 is located soas to face the movable contact 52. One end of the heater coil 56 iselectrically connected to the support 24 by means of a suitableelectrical conductor 58, and the other end thereof is electricallyconnected to the conductor 40.

The system as shown is in the normal unheated position with switch Sopen and contacts 50 disconnected from each other. In this position itwill be noted that the contact 29 engages the contact 22. By placing thevessel 8 upon the heating coil 2 the sensor plate 12 is depressed, butdoes not have any effect upon the engagement of the contacts 20 and 22.By moving the handle 43 of the switch S to the closed position theheater coil 36 is directly connected across supply lines N and L bymeans of the circuit comprising conductor 41, heater coil 36 and theconductors 3d, 4d and 6. Such current flow will immediately causeheating of the heater coil 36. The magnitude of such current how will bedependent, however, upon the position of the variable resistor 48- 46connected across the heater coil 36.

At the same time switch S is closed, it will be noted that the heatercoil 56 is directly connected across supply lines L and N by means ofconnected conductors 6, 4i!- and conductor 58, support 24, engagedcontacts 2022, bimetal 16 and conductor 41. By means of the current flowthrough the heater coil 56 the bimetal 55 will expand to cause it freeend to engage the cont-act 52 and move the contact 52 into bridgingrelationship with the spaced contacts 50 whereby the heater coil 2 willbe connected across the supply lines L and L by means of the circuitcomprising conductor 4, having electrically bridged contacts 50 therein,and conductor 6, having the closed switch S there-in. As soon as heatingof the heating element 2 occurs heat will be transmitted to the vessel 8and its contents, which in turn, will cause heat to be transmitted tothe sensor plate 12 and the sensor bimetal 14 secured thereto.

Such heat flow through the vessel will tend to cause the sensor bimetal14 to move counterclockwise as described. counterclockwise movement ofthe sensor bimetal 14 will, in turn, cause counterclockwise movement ofthe control bimetal 16'which is mechanically secured thereto. Suchcounterclockwise movement of the bimetal 16 will occur until the sensorbimetal 14 has received sufiicient heat so that it movescounterclockwisea sufiicient distance to overcome the contact pressure between thecontacts 20 and '22 whereby the contact 20 will move away from thecontact 22. Of note, however, is the fact that as the heater coil 36 hasbeen heated during this period and as the deflection of the heatedbimetal 16 is to close the contacts 20 and 22, it is necessary for thesensor bimetal 14 'toreceive sufficient heat to overcome this effect ofthe heated bimetal 16, in addition to the initial contact pressurebetween the contacts 20 and 22. Upon separation of contacts 20 and 22the heater coil 56 will be disconnected from the supply lines L and N,so that bimetal 54 will no longer be heated and will start to lose itsheat to the surrounding air. When bimetal 54 has cooled sufficiently itwill move away from the contact 52 and cause the movable contact 52 tomove out of engagement with the spaced contacts 50, whereby the heaterelement 2 will-be disconnected from the supply lines L and L and, inturn, will start to cool.

As has been indicated the contact 22 initially engages he contact 20 sothat an initial pressure exists therebetween. The pressure of suchinitial engagement determines a portion of the force which must beovercome by the sensor bimetal 14 as described above. However, byvarying the initial pressure between the contacts 29 and 22 aspreviously described, the total force which must be overcome by thesensor bimetal 14 may be varied and consequently the operatingtemperature of the sensor bimetal 14 may be varied.

Cooling of the heating element 2 will cause the vessel 8 and itscontents to cool, and in turn, the sensor bimetal 14 will be cooled.Upon such cooling of the sensor bimetal 14. the sensor bimetal 14 willmove clock-. wise so as to reestablish engagement of the contacts 20 and22 by moving the contact 22 toward contact 2%). it will be noted howeverthat the heater coil 36 is not disconnected from the supply lines L andN as long'as the switch S remains closed so that the bimetal 16 has afixed clockwise elfect regardless of whether the contacts 20 and 22 arein or out of engagement with each other. Thus, the action of the bimetal16 aids in the reengagement of the contacts 20 and 22.

The effect of the heater coil 36 can also be understood by consideringthe circuit without any heat being supplied by the heating coil 36. Insuch event when the sensor bimetal 14 receives sufiicient heat it willmove counterclockwise so as to cause separation of the contacts 2t) and22, and in turn as indicated, heating element 2 is deenergized. Upondeenergization of heater element 2 the vessel 8 is cooled and the sensorbimetal 14 is cooled and urges the contact 20 into engagement with forcemust be exerted by the sensor bimetal 14 before cycling of the devicewill occur.

By supplying the heating coil 36 with heat, contact 20 is urged towardcontact 22 so that the sensor bimetal 14, in this case, must beadditionally heated to obtain counterclockwise movement which issufiicient to obtain separation of the contacts 20; and 22 than in thecase where no heat is supplied to the bimetal 16. Accordingly, as moreheating of the sensor bimetal 14 is required a higher cyclingtemperature maybe achieved. In view of the fact that the variableresistor 46-48 has an infinite number, within limits, of positions itcan be seen that the cycling temperatures may readily be varied betweena wide range of values as each setting of the variable resistor 46-48will cause a change in the current flowing through the heating coil 36,and, consequently, a change in the heating rate of the bimetal 16.

.As is also well known in the art of thermostatic 'matee rial, arelationship exists between the thickness and length of two.thermostatic elements so that for the same temperature in both elementsthere is no movement of the bimetals with respect to each other. Suchsystems are usually referred to as being ambient compensated" and may beemployed in the device as described in order to prevent changes incontact pressure under the various ambient temperature conditions inwhich the device functions. Thus, a thermal balance can be achievedbetween the sensor bimetal 14 andthe bimetal 16 so that the two bimetals14 and 16 will be at substantially the same temperature at the controltemperature at which thecontacts 2th and 22 separate. By obtaining sucha thermal balance there is no transient heat transfer between the twobimetals 14 had 16. In terms of deflece tion, the deflection of thesensor bimetal 14 is balanced by the deflection of the bimetal 16 at thecontrol temperature. It, of course, is to be realized that the contactpressure between the contacts 20 and 22 will affect the controltemperature, that is, increasing the contact presbe obtained.

sure raises the control temperature. However, by initially settingcontact 20 to just engage contact 22 at room temperature the abovethermal balance can readily It will also be noted that although thecontrol temperature is controlled by both the bimetals 14 and 16functioning as described, the cycling action of the device is performedby the sensor bimetal 14 only, so that the bimetal 14 may properly bereferred to as a cycler bimetal.

Having described a preferred embodiment of my invention in accordancewith the patent statutes, it is desired that the invention be notlimited to the specific construction shown, inasmuch as it is apparentthat modifications thereof maybe made without departing from the broadspirit and scope of my invention, Thus, for example, the various methodsof varying the current through the heater coil 36 as shown in mycopending application entitled Control Device filed concurrentlyherewith Serial No. 628,383 and which application has been assigned tothe same assignee as this invention, may be used. Accordingly, it isdesired that the invention be interpreted as broadly as possible, andthat it be limited only as required by the prior art.

I claim as my invention:

1. A control device for controlling the temperature of a cooking vesseland its contents by means of controlling an electrical resistanceheating unit therefor comprising, a high thermal conductivity portionfor engagement with a cooling vessel and having a first control portionwhich is movable with relation to said thermal portion in response totemperature changes in said thermal portion, a second control portion,supporting means supporting said second control'portion from said firstcontrol portion so as to be electrically and thermally insulatedtherefrom, means connected to said second control portion forcontrolling the energization of a resistance unit in response tomovement of said first and second control portions, and an auxiliaryelectrical heater supported with respect to said second control portionto cause movement thereof.

2. A control device for controlling the temperature of a cooking vesseland its contents by means of controlling an electrical resistanceheating unit therefor comprising, a high thermal conductivity portionfor engagement with a cooling vessel and having a first control portionwhich is movable with relation to said thermal portion in response totemperature changes in said thermal portion, a second control portion,support means supporting said second control portion from said firstcontrol portion so as to be electrically and thermally insulatedtherefrom, means connected to said second control portion forcontrolling the energization of a resistance unit in response tomovement of said first and second control portions, an auxiliaryelectrical heater supported with respect to said second control portionto cause movement thereof, and a variable electrical resistanceconnected with respect to said electrical heater to vary the magnitudeof the current through said heater whereby the time required formovement of said second control portion is varied.

3. A control device for controlling the temperature of a cooking vesseland its contents by means of controlling an electrical resistanceheating unit therefor comprising, a high thermal conductivity portionfor engagement with a cooling vessel and having a first control portionwhich is movable with relation to said thermal portion in response totemperature changes in said thermal portion, a second control portion,support means supporting said second control portion from said firstcontrol portion so as to be electrically and thermally insulatedtherefrom, means connected to said second control portion forcontrolling the energization of a resistance unit in response tomovement of said first and second control portions, an auxiliaryelectrical heater supported with respect to said second control portionto cause movement thereof,

said first control portion being movable when heated to preventenergization of a resistance unit, said second control portion beingmovable when heated in a direction opposite to that of said firstcontrol portion when heated, and a variable electrical resistanceconnected with respect to said electrical heater to vary the magnitudeof the current through said heater whereby the time required formovement of said second control portion is varied. 4. A control devicefor controlling the temperature of a cooking vessel and its contents bymeans of controlling the heat output of a heating unit thereforcomprising, a high thermal conductivity portion for engagement with acooling vessel and having a first control portion which is movable withrelation to said thermal portion in response to temperature changes insaid thermal portion, a second control portion, support means supportingsaid second control portion from said first control portion so as to beelectrically and thermally insulated therefrom, means connected to saidsecond control portion for controlling the heat output of a heating unitin response to movement of said first and second control portions, anauxiliary electrical heater supported with respect to said controlportion to cause movement thereof, and a variable electrical resistanceconnected with respect to said electrical heater to vary the magnitudeof the current through said heater whereby the time required formovement of said control portion is varied.

5. A control device for controlling the temperature of a cooking vesseland its contents by means of controlling an electrical resistanceheating unit therefor comprising, a sensor plate of a heat conductingmaterial, a first bimetallic member thermally secured to said sensorplate so as to have at least a portion thereof movable with respect tosaid sensor plate, a second bimetallic member, support means forsupporting said second bimetallic member from said portion of said firstbimetallic member so as to be electrically and thermally insulatedtherefrom, a pair of contacts one of which is mechanically connected tosaid second bimetallic member to be movable into and out of engagementwith the other in response to movement of said first and secondbimetallic members, an electrical resistance heater supported withrespect to said second bimetallic member to cause movement thereof, andelectrical circuit means electrically connected to each of said contactsfor controlling the electrical energization of an electrical resistanceunit.

6. A control device for controlling the temperature of a cooking vesseland its contents by means of controlling an electrical resistance unitcomprising, a sensor plate of a heat conducting material, a firstbimetallic member thermally secured to said sensor plate so as to haveat least a portion thereof movable with respect to said sensor plate, asecond bimetallic member, support means for supporting said secondbimetallic member from said portion of said first bimetallic member soas to be electrically and thermally insulated therefrom, a pair ofcontacts one of which is mechanically connected to said secondbimetallic member to be movable into and out of engagement with theother in response to movement of said first and second bi etallicmembers, an electrical resistance heater supported with respect to saidsecond bimetallic member to cause movement thereof, a variableelectrical resistance connected with respect to said heater to vary themagnitude of the current through said heater whereby the time requiredfor said one contact to move into and out of engagement with said othercontact is varied, and electrical circuit means electrically connectedto each of said contacts for controlling the electrical energization ofan electrical resistance unit.

7. A control device for controlling the temperature of a cooking vesseland its contents by means of controlling an electrical resistance unitcomprising, a sensor plate, a sensor bimetal thermally secured to saidsensor plate with a portion thereof being movable in response totemperature changes of said sensor plate, a control bimetal, electricaland thermal insulating means supporting said control bimetal from saidmovable portion of said sensor bimetal, a pair of normally engagedcontacts one of which is mounted on said control bimetal so as to bemovable in and out of engagement with the other, an electrical. heatermounted on said control bimetal to cause movement thereof toward theother of said contacts, and means for supporting said'other contact infixed relationship with said sensor plate and electrically insulatedtherefrom.

8. A control device for controlling the temperature of a cooking vesseland its contents by means of controlling an electrical resistance unitcomprising, a sensor plate, a sensor bimetal thermally secured to saidsensor plate with at least a portion extending outwardly therefrom so asto be movable with respect to said sensor plate, an elongated controlbimetal in alignment with and having one of its ends spaced from saidmovable portion of said sensor bimetal, electrical, thermal insulatingmeans for supporting said control bimetal from said movable portion ofsaid sensor bimetal, a pair of normally engaged contacts one of which ismounted on said control bimetal, and an electrical heater elementmounted on said control bimetal for causing movement thereof toward theother of said contacts.

9. A control system operatively associated with and adapted to controlan electrical resistance unit comprising, a control circuit having inputand output terminals adapted to be connected to a suitable source ofelectrical energy and an electrical resistance unit, respectively,switch means in said circuit for connecting said input terminals to saidoutput terminals, an electrical resistance heating element connected tosaid circuit independently of said switch means, a heat actuated memberlocated to be heated by said heating element; operating means connectedin parallel with said heating element, normally engaged separablecontacts electrically connected in series in said parallel circuit oneof which is mechanically connected to said heat actuated member, saidactuated memberbeing movable when heatedto move said one contact towardthe other of said contacts, another heat actuated member disposed to beheatedby an electrical resistance unit, said other heat actuated memberbeing thermally insulated from and mechanically connected to saidfirst-mentioned actuated member to move said one contact out ofengagement with said other contact when said last-mentioned actuatedmember is heated whereby said operating means is deenergized. v

10. A control system operatively associated with and adapted to controlan electrical resistance unit comprising, a control circuit having inputand output terminals adapted to be connected to a suitable source ofelectrical energy and an electrical resistance unit, respectively,switch means in said circuit for connecting said input terminals to saidoutput terminals, an electrical resistance heating element connected tosaid circuit independently of said switch means, a heat actuated memberlocated to be heated by said heating element; operating means connectedin parallel with said heating element, normally engaged separablecontacts electrically connected in series in said parallel circuit oneof which is mechanically connected to said heat actuated member, saidactuated member being movable when heated to move said one contacttoward the other of said contacts, another heat actuated member disposedto be heated by an electrical resistance unit, said other heat actuatedmember being thermally insulated from and mechanically connected to saidfirstrnentioned actuated member to move said one contact out ofengagement with said other contact when said lastmentioned actuatedmember is heated whereby said operating means is deenergized, and meansin said first-mentioned circuit for varying the current flow throughsaid heating element. p

11. A control system operatively associated with and adapted to controlan electrical resistance unit comprising, a control circuit having inputand output terminals adapted to be connected to a suitable source ofelectrical energy and an electrical resistance unit, respectively,

switch means in said circuit for connecting said input terminals to saidoutput terminals, an electrical resistance heating element connected tosaid circuit independently of said switch means, an elongated firstheat-actuated member located to be heated by said heating element, asecond heat-actuated member located to be heated by an electricalresistance unit having one of its ends spaced from one end of said firstheat-actuated member, thermal insulating means for mechanicallyconnecting adjacent ends of said members, operating means connected inparallel with sm'd heating element, and separable contacts electricallyconnected in series in said parallel circuit one of which ismechanically connected to the other end of said first heat-actuatedmember so as to be movable into and out of engagement with the other ofsaid contacts to control the energization of said operating means.

I 12. A controlsystem operatively associated with and adapted to'controlan electrical resistance unit comprising, a control circuit having inputand output terminals adapted to be connected to a suitable source ofelectrical energy and an electrical resistance unit, respectively, apair of electrical resistance heating elements connected in parallel tosaid circuit, heat-actuated members located adjacent said elements,respectively, so as to be heated thereby, a pair of separable contactsin said parallel circuit one of which is mechanically connected to oneof said members to control the energization of the element for the otherof said members, another heat-actuated member located to be heated by anelectrical resistance unit having one of its ends spaced from said onemember, thermal insulating means for mechanically connecting adjacentends of said one and another member, said one and another member beingmovable when heated to move said one contact on said one memberinto andout of engagement with the other of said contacts, switch means forconnecting and disconnecting said input terminals to said outputterminals, and said other member comprising operating means for saidswitch means.

13. A control system operatively associated with and adapted to controlan electrical resistance unit comprising, an energizing circuit adaptedto be connected to an electrical resistance unit, said energizingcircuit having 9. normally open switch means therein, a heater elementand a variable resistance connected in parallel in said circuit sothatcurrent will normally flow therethrough, a heatact uated memberarranged to ;;be heated by said heater element and which is electricallyconnected to said heater element, said heat-actuated member normallyengaging Contact means to connect switch operating means in parallelwith said heater element whereby said normally open switch means isclosed, said heat-actuated member being movably supported so that uponheating said contact means is disengaged thereby and said switchoperating means is deenergized, and said variable resistance beingoperable to vary the heat output of said heater whereby the timerequired for closing said switch means may be varied.

14. A control system operatively associated with and adapted to controlan electrical resistance unit comprising, an energizing circuit adaptedto be connected to an electrical resistance unit, said energizingcircuit having a normally open switch means therein, a heater elementand a variable resistance connected in parallel in said circuit so thatcurrent will normallyflow therethrou-gh, a heatactuated member arrangedto be heated by said heater element and which is electrically connectedto said'heater element, said heat-actuated member normally engagingcontact means to connect switch operating means in parallel with saidheater element whereby said normally open switch means is closed, saidheat-actuated member being movably supported so that upon heating saidcontact means is disengaged thereby and said switch operating means isdeenergized, said variable resistance being operable to vary the heatoutput of said heater whereby the time required for closing said switchmeans may be varied, and another heat-actuated member responsive tothermal energy externally of said circuit arranged to move saidfirst-mentioned heat-actuated member in a direction opposite that inwhich said first-mentioned heat-actuated member moves when heatedwhereby said switch operat ing means is deenergized and said switchmeans is opened.

15. A control system operatively associated with and adapted to controlan electrical resistance unit, a control circuit havinginput and outputterminals adapted to be connected to a suitable source of electricalenergy and an electrical resistance unit, respectively, a sensor bimetalhaving a fixed portion and a remote portion movable with respect to saidfixed portion, an elongated control bimetal spaced from the remoteportion of said sensor bi- 7 metal, thermal insulating means formechanically securing one end of said control bimetal to said remoteportion of said sensor bimetal, a pair of normally engaged separablecontacts connected to said circuit one of which is mounted adjacent theother end of said control bimetal, switch means in said circuit forconnecting said input terminals to said output terminals having anoperating means connected in series with said contactsin said circuit,said sensor bimetal being movable when heated to cause separation ofsaid contacts, and heating means in said circuit adjacent said controlbimetal for causing movement of said control bimetal toward the other ofsaid contacts.

16. A control device for controlling the temperature of a cooking vesseland its contents by means of controlling an electrical resistanceheating unit therefor comprising, a high thermal conductivity portionfor engagement with a cooking vessel and having a first control portionwhich is movable with relation to said thermal portion in response totemperature changes in said thermal portion, a second control portion,support means supporting said second control portion from said firstcontrol portion, means actuated by said second control portion forcontrolling the energization of a resistance unit in response tomovement of said first and second control portions, an auxiliaryelectrical heater supported with respect to said second control portionto cause movement thereof, and a variable electrical resistanceconnected with respect to said electrical heater to vary the magnitudeof the current through said heater whereby the time required formovement of said second control portion is varied.

References Cited in the file of this patent UNITED STATES PATENTS BletzApr 30, 1946 Clark Sept. 23, 1947 Akeley Oct. 3, 1950 Akeley Aug. 12,1952 Fry May 11, 1954 Weeks Dec. 10, 1957

